1. Field of the Invention
This invention relates to a radiation reactor. In particular, the present invention relates to a radiation reactor construction which is especially suited to the effective irradiation of a fluid passing through the radiation reactor.
2. Background
Throughout this specification, the term “radiation reactor” shall be understood to encompass any type of device comprising a light source whose radiation is used to irradiate, treat and/or react with a fluid, which fluid is directed through the device so as to pass within the radiation transmission range of the light source.
The radiation reactors of the present invention are typically used with ultra-violet light sources. These ultra-violet radiation reactors are used to perform a plurality of functions such as the generation of ozone, partial or full sanitisation of contaminated fluids and the like, in particular water, including rainwater, surface water, borehole water, well water and municipal water.
Ultra-violet radiation having a wavelength of approximately 254 nm is known to be ideal for the germicidal treatment of liquids. For example, rainwater carrying some potentially harmful impurities may be treated by subjecting the rainwater to ultra-violet radiation having a wavelength of approximately 254 nm. The radiation reactor of the present invention is envisaged to be used within a water treatment process and apparatus, such that the ultra-violet radiation from the ultra-violet light source, or ultra-violet lamp, irradiates and thus partially sanitises water which is passed through the ultra-violet radiation reactor.
The intensity of the ultra-violet radiation from an ultra-violet lamp decreases over distance. As a consequence it is preferable to subject the fluid to the ultra-violet radiation as close as possible to the ultra-violet lamp. Indeed, in many instances, for legal, regulatory and/or best practice reasons it will be essential for manufacturers of radiation reactors to ensure that the amount of radiation which a fluid passing through their radiation reactor is subjected to, is sufficiently high so as to meet with designated requirements. Taking the example of irradiating rainwater with UV light, in order for efficient UV radiation treatment of the rainwater to be adjudged to have taken place, it is generally recommended that the rainwater be subjected to ultra-violet radiation at a fluence rate of 40 mWs/cm2 in accordance with best practice and current prevailing regulations, for example, USEPA Guide Standard and Protocol for Testing Microbiological Water Purifiers, April 2006.
An ultra-violet radiation reactor of the type referred to hereinbefore will typically comprise of an ultra-violet light source, alternatively referred to as an ultra-violet lamp, and a fluid receiving casing. The ultra-violet lamp will be mounted within the fluid receiving casing. In most instances the casing will be tubular and the ultra-violet lamp will be an elongated lamp or series of lamps. The ultra-violet radiation reactor will be installed in a vertical orientation with the longitudinal axes of both the tubular casing and the elongated ultra-violet lamp being co-axial and substantially vertical after installation of the ultra-violet radiation reactor.
As mentioned hereinbefore, the ultra-violet light source is generally co-axial with the liquid receiving tube so that the liquid can surround the ultra-violet light source as it flows along the length of the tube, thus increasing the exposure of the liquid to the ultra-violet light source. In essence, a substantially annular shape is created intermediate the ultra-violet elongated lamp and an inner wall of the tubular casing, through which annular space the fluid passes as it is passed through the ultra-violet radiation reactor.
In some cases, a protective quartz sleeve may be used to protect the ultra-violet lamp from damage through direct contact with the fluid. In such embodiments, it will be understood that the substantially annular space is thus created intermediate the protective sleeve and the inner wall of the tubular casing.
In order to subject the fluid to the ultra-violet radiation as close as possible to the ultra-violet lamp, the distance between the ultra-violet lamp and an outermost point within the substantially annular space created within the radiation reactor should be kept to a minimum by decreasing the distance as much as possible. However, in decreasing the distance between the ultra-violet light source and the outermost point within the substantially annular space, the width of the substantially annular space is decreased and this results in a narrowing of the channel through which the fluid must pass. Therefore the flow rate of the fluid through the ultra-violet reactor will be lowered; there is a trade-off between the flow rate of the fluid passing through the ultra-violet reactor and the effectiveness of the ultra-violet reactor in that a widening of the width of the annular space will increase the size of the channel through which the fluid will flow, but will also reduce the effectiveness of the radiation as the fluid at the outermost point within the substantially annular space will be subjected to a radiation with a lower intensity. If the fluid is subjected to too low an intensity, then prevailing legal, regulatory, certification and best practice requirements may not be met. The width of the annular space is therefore largely dictated by the necessary radiation intensity, and the overall diametric size of the tubular casing will be restricted accordingly. This restriction will lower the flow rate of the fluid through the radiation reactor.
To obviate the restriction on flow rates, it is known from the prior art to increase the flow rate by forcing the fluid through the ultra-violet reactor at a higher flow rate than would normally occur under normal system pressures, or under gravity. However, such a solution requires the ultra-violet reactor to be relatively long so that the fluid, which is flowing at a relatively high flow rate, is still exposed to a sufficient amount of ultra-violet radiation so that the fluid is treated. This is problematic as the ultra-violet reactor will increase in length and become less compact. The length of such relatively long reactors is also limited by the availability of ultra-violet lamps of sufficient length.
As it is preferable that the length of the ultra-violet reactor be minimised for compactness and indeed due to technical limitations involving ultra-violet lamps, it is desirable that the relatively high flow rate be achieved through short ultra-violet reactors which do not suffer from ineffective ultra-violet radiation treatment problems mentioned above.
A number of solutions have been proposed to achieve relatively high flow rates through relatively short ultra-violet radiation reactors, without suffering from ineffective or insufficient ultra-violet radiation.
An example of an ultra-violet radiation reactor, which has been designed to increase the effectiveness of the ultra-violet radiation, can be found in PCT Patent Publication Number WO92/10429 (KLAUSEN). PCT Patent Publication Number WO92/10429 discloses an ultra-violet irradiator which comprises an ultra-violet lamp inserted inside of a quartz tube, which in turn is mounted within the irradiator. The quartz tube is used to protect the ultra-violet lamp from damage by the liquid. Ultra-violet radiation emitted from the ultra-violet lamp passes through the quartz tube and irradiates liquid which passes between the quartz tube and the outer casing of the irradiator. The liquid is fed into the irradiator through an inlet pipe and is directed around the quartz tube in a helical path by a helicoid guide plate. As the helicoid guide plate causes the liquid to travel in a helical path around the lamp, it is claimed that the liquid is effectively disinfected. The helicoid guide plate extends across between the quartz tube and the outer casing of the irradiator such that it defines a spiral channel which the liquid flows within. This spiral channel effectively increases the length of the flow channel within the tubular casing and causes the fluid passing through the channel to be exposed to the radiation for a longer period of time than would otherwise have been the case if the fluid passed straight through the outer casing.
A problem with the ultra-violet irradiator disclosed in PCT Patent Publication Number WO92/10429 is that as the liquid is passed around the quartz tube, the liquid which is at, diametrically speaking, outer parts of the spiral channel, will travel at faster rates than the liquid at inner parts of the spiral channel, due to the centrifugal effect acting on the liquid. Therefore, the liquid in these outer parts of the spiral channel will spend less time in the radiation reactor. Moreover, as the intensity of the ultra-violet radiation from the lamp decreases over distance, the liquid at these outer parts of the helical path, travelling at faster rates and spending less time in the radiation reactor, will also be subjected to ultra-violet radiation of lower intensity than the liquid at inner parts of the spiral channel. As a consequence, the liquid at the outer parts of the spiral channel will not be subjected to the same amount of ultra-violet radiation as the liquid at the inner parts of the helical path, because the liquid at the outer parts of the helical path will flow through the irradiator faster and will also be subjected to ultra-violet radiation of lower intensity.
Ultra-violet reactors using spiral pathways and spiral channels are also disclosed in U.K. Patent Publication Number GB 2404318A and GB 2404319A (both in the name of JOHN MANUFACTURING LIMITED). GB 2404318A discloses a combination photo-electronic water purifier comprising a UV irradiator within a housing. The water purifier comprises a rifled channel which stretches all the way through the housing. The water purifier disclosed is defined to be rifled in the sense that it comprises a plurality of generally helical ribs which project into the treatment chamber between the sheath which protects the UV light tube and the cylindrical bore of the housing, so as to produce a spiral motion in the water flowing along the annular treatment chamber from an inlet of the water purifier to an outlet of the water purifier. GB 2404319A discloses a combination photo-electronic air purifier comprising a negative ion generator, a UV irradiator and an illuminator, switched on or off by an infra-red remote control. The air purifier has a rifled air duct, where an extreme-UV light tube is fitted inside the rifled channel. The rifled channel causes the air to spiral around the UV light tube.
Both GB 2404318A and GB 2404319A describe indentation or protrusions which are used to cause a spiraling motion to the fluid passing through the reactor. This spiraling motion causes the fluid at outermost parts of the casing of the reactors to flow at faster rates in comparison with the fluids at more centrally located parts of the casing. This is due to the centrifugal effect acting on the fluids as there are spiraled around the reactors due to the indentations and protrusions. Therefore, the fluids in the outer parts spend less time in the radiation reactor, and, are subjected to radiation of a lower intensity. Thus, the fluids at the outer parts of the casing which are spiraling around as a result of the design of the casings will not be subjected to the same amount of radiation as a result of flowing through the reactor faster and being subjected to radiation of a lower intensity.
Another example of a radiation reactor is shown in PCT Patent Publication Number WO02/076517 A1 (TISSI). PCT Patent Publication Number WO02/076517 discloses a device for the sterilisation and/or purification of a fluid. In particular, the device is designed to be used on fluids which are part of a compressed or forced air flow. The device has a casing and at least one ultra-violet radiation lamp housed inside the casing. The device is designed to be compact in size whilst also increasing the time during which the fluid flowing through the device will be exposed to the sterilising action of the ultra-violet radiation lamp. To achieve this, the casing of the device houses so-called “conveying means”. The conveying means is helicoidally wound coaxially around a tubular element which protects the ultra-violet radiation lamp. The conveying element is wound around the tubular element for substantially the entire length of the tubular element. In this manner, a spiral-shaped channel is created for the fluid to flow through.
As before, due to the use of a spiral channel, the fluid flowing around the spiral channel will spend a longer amount of time within the device, however, the fluid particles at the outer portions of the spiral-shaped channel, adjacent the casing, will travel faster due to the centrifugal forces acting upon them, whilst at the same time, those faster moving particles will be subjected to radiation of a lower intensity due to their distance from the ultra-violet lamp. As before, these particles will thus spend less time in the reactor and will be exposed to lower intensity radiation, and it is therefore possible that the particles will not be sufficiently irradiated or treated so as to meet with legal, regulatory, certification or best practice requirements in a jurisdiction.
The problems which are found with the ultra-violet irradiators disclosed in PCT Patent Publication Number WO92/10429, U.K. Patent Publication Number GB 2404318A, U.K. Patent Publication Number GB 2404319A, and, PCT Patent Publication Number WO02/076517 are also experienced in radiation reactors which do not have spiral channels, but do have rotational flow of the fluid within the radiation reactor casing due to, inter alia, a tangentially arranged fluid inlet.
Tangentially arranged fluid inlets are preferable for imparting a velocity to the fluid entering the radiation reactor so as to create a relatively high flow rate through the radiation reactor. In the cases where a fluid enters a radiation reactor, tangentially through an inlet that is of small diameter relative to the radiation reactor casing, it has been observed that the fluid adjacent outer walls of the reactor casing tends to flow rapidly through the reactor with a relatively low exposure to the radiation. Whereas, fluid near a central longitudinal axis of the radiation reactor casing will tend to be prohibited from flowing out of the reactor due to an upwelling of the fluid in a central portion of the substantially annular space within the radiation reactor casing. Thus, radiation reactors with tangentially arranged fluid inlets suffer the same problems regarding the effectiveness of the radiation of the fluids passing through such radiation reactors.
It is known that in typically annular UV irradiation systems that “UV shadowing” may occur. UV shadowing occurs where micro-organisms can be protected from the effects of the UV irradiation by the fact that they may be attached to or behind UV non-transparent particles and are therefore protected or shadowed from the UV irradiation by the particle. The result is that they may not receive the correct dose of UV irradiance to cause their inactivation and may therefore pass through the UV reactor in an active living state.
It is a goal of the present invention to provide a radiation reactor which overcomes at least one or more of the above mentioned problems. In particular, it is desired to design a radiation reactor which allows relatively quick flow rates, with compact design and can still ensure sufficient and proper radiation of fluids passing through the reactor.
It is a further goal of the present invention to provide a method of radiating a fluid in a radiation reactor which overcomes at least one or more of the above mentioned problems. In particular, it is desired to provide a method of radiating a fluid which allows relatively quick flow rates through the radiation reactor, with a relatively compact design of the reactor whilst still ensuring sufficient and proper radiation of fluids passing through the reactor.